1. Technical Field of the Invention
The present invention relates to a device for controlling the phase angle between a first and a second crankshaft of an internal combustion engine of the type that includes at least one primary cylinder that communicates with at least one secondary cylinder. A primary piston is normally included that is movably arranged in each primary cylinder and is connected to the first crankshaft. In every secondary cylinder, there is a secondary piston movably arranged that is connected to the second crankshaft. The first and second crankshafts are typically connected to each other by means of a transmission and a means or mechanism for obtaining a phase shift control. A crankshaft extension is also provided for the phase angle control, and which is fixedly connected against relative rotation to one of the crankshafts, and rotationally connected to the second of the crankshafts.
2. Background Art
In internal combustion engines of the piston type, for example Otto engines and diesel engines with one or several cylinders with pistons reciprocating therein, a fuel air mixture is compressed in a combustion chamber, where it is ignited and burnt when the piston is in its uppermost position.
The compression of the fuel air mixture is determined by the compression ratio of the particular engine in question, a parameter that is defined as the ratio between the volume in the cylinder when the piston is in its lowest and uppermost positions. Modern Otto engines usually have a compression ratio around 10:1 (compression FIG. 10), while supercharged engines, for example turbo engines, have a lower ratio and diesel engines have a considerably higher compression ratio. The compression ratio of the engine affects the combustion of the fuel air mixture.
A high compression contributes to an effective combustion, which in turn contributes to a high efficiency and low fuel consumption. At the same time, however, there is a need for using high octane fuel, particularly in the case of high engine loads in order to avoid uncontrolled combustion. In view of this background, it becomes evident that it can be desirable to be able to vary the compression ratio during engine operation depending on fuel quality and engine load.
U.S. Pat. No. 5,638,777 discloses an internal combustion engine with a variable compression ratio. The engine has a number of primary cylinders and a corresponding number of secondary cylinders which each communicates with a corresponding primary cylinder. In each primary cylinder, a primary piston is connected to a first crankshaft and is arranged to carry out back and forth movement. In a corresponding way, in each secondary cylinder there is a secondary piston connected to a second crankshaft, the secondary piston also being arranged to carry out back and forth movement. Between the first and second crankshafts, there is arranged a gear wheel transmission and a device for phase angle shift between the shafts, with the purpose of obtaining a compression ratio that depends on the current load of the engine. The device includes a driving shaft fixedly connected to the second crankshaft, and which is equipped with spiral-shaped splines concentrically arranged inside an outer casing. The outer casing exhibits a first gear wheel intended to interact with a second gear wheel arranged on the first crankshaft, and that has internal spiral-shaped splines. Between the outer casing and the drive shaft, there is arranged a displaceable pipe element, the enveloping surface of which is equipped with spiral-shaped splines intended to cooperate with the internal spiral-shaped splines of the outer casing. The pipe element is, in addition, equipped with internal spiral-shaped splines that cooperate with the spiral-shaped splines arranged on the drive shaft. In the case of axial displacement of the pipe element, for example in the case of a hydraulic control system, a phase angle shift is obtained between the first gear wheels and the drive shaft, and thus also between the first and second crankshafts.
Although the device exhibited in U.S. Pat. No. 5,638,777 enables good control of the phase shift between the crankshafts, it does have certain drawbacks. One drawback is that it is relatively expensive to manufacture it, since it is relatively complex in its design, especially concerning the displaceable pipe element, which is equipped both on the enveloping surface and internally with spiral-shaped splines. Another drawback is that the pipe element, including the hydraulic control system, needs a relatively large accommodating space in its axial direction. This makes it difficult to install it in cars with lateral multi-cylinder engines. Furthermore, assembly/disassembly of this device is relatively difficult to carry out.
An object of the present invention is to provide a device for controlling the phase angle between a first and second crankshaft of an internal combustion engine, which, relative to previous technology, is more cost efficient to manufacture.
In an exemplary embodiment, such a device includes at least one primary cylinder which communicates with at least one secondary cylinder and which has a primary piston that is movably arranged in that primary cylinder. The primary piston being connected to the first crankshaft, and in every secondary cylinder there is movably arranged a secondary piston that is connected to the second crankshaft. The first and second crankshafts are connected to each other by means of a transmission and the device further includes means for obtaining the phase shift control and a crankshaft extension intended for such phase control. The extension is connected fixed against rotation to one of the crankshafts, and rotationally fixed to the other of the crankshafts. By means of the crankshaft extension being displaceably arranged relative to one of the crankshafts, a mechanical interface is obtained at which phase angle shift can be done without introducing further components.
According to a preferred embodiment, the inventive means or arrangement is configured to bring about axial displacement of the crankshaft extension, and as a result of which the phase angle will shift. The means or arrangement preferably consists of a hydraulic piston arranged in a housing for affecting the crankshaft extension in at least one direction. This enables quick phase angle shift with good precision at high engine loads.
According to another preferred embodiment, the hydraulic piston is also arranged to affect crankshaft extension in a second direction, to enable optimal control of the phase angle between the first and second crankshaft, for example in the case of rapid shifts in engine load.
Since the hydraulic piston according to the present invention is arranged to not rotate relative to the housing, a simplified oil sealing is obtained between the piston and the housing. Furthermore, this creates favorable conditions for obtaining a simple and durable arrangement for supplying oil to the piston.
In another preferred embodiment of the invention, the crankshaft extension, at one end, is equipped with splines that enable a displaceable connection, fixed against rotation, to one of the crankshafts. The crankshaft extension is, additionally, at its other end, equipped with a grooved portion, preferably trapeze grooves, for the rotatable connection.
By providing the crankshaft extension according to the present invention with a flange between the spline-equipped portion and the grooved portion which the hydraulic piston is arranged to affect, a compact and axially short device for controlling the phase angle is enabled; an attribute that is extremely advantageous in most motor vehicles.